The present invention concerns concrete slipform paving machines that have a propelling unit or tractor from which a paving kit is suspended with which a layer of concrete is shaped and finished over the underlying ground as the tractor travels along a road or airfield alignment. The tractor of a concrete slipform paver has a rectilinear frame which straddles the concrete roadway or airfield pavement section that is being paved. The frame is propelled and supported on either end by crawler tracks mounted on side bolsters. These side bolsters each typically have two hydraulic supporting jacking columns, each of which connects to a crawler track, that allow the tractor frame elevation to be manually or automatically varied relative to the ground. The frame, and in particular a center module thereof, supports a diesel engine-driven hydraulic power unit which supplies power to the tractor and the paving kit.
The paving kit is conventionally suspended below the tractor frame by mechanical means, such as with hooks and a locking mechanism. The paving kit takes its hydraulic power from the power unit on the tractor. The tractor and the paving kit pass over fresh concrete placed in and distributed over its path as a relatively even and level mass that can be conveniently slipform-paved. During this process, the tractor-attached paving kit spreads the semi-solid concrete dumped in the path of the paver, levels and vibrates it into a semi-liquid state, then confines and finishes the concrete back into a semi-solid slab with an upwardly exposed and finished surface. The sideforms mounted on each side of the slipform paving kit shape and confine the sides of the slab during the slipform paving process. Other kits can be attached to these tractors such as kits for conveying and spreading concrete and trimming and spreading base materials.
The tractor normally has four crawler tracks, but can also have only three, each mounted to a jacking column, supporting and propelling the frame during use of the paver in the paving direction. The jacking columns are carried on the bolsters, or on bolster swing legs connected to the fore and aft ends of the side bolsters, that are pivotable about vertical axes to change the relative position of the crawlers for a variety of reasons and/or for changing the movement correction of the crawlers and therewith of the paving machine during use. The bolster swing legs with jacking columns and crawlers can also be relocated and mounted directly to the front and rear of the tractor center module, to the outside of the side bolsters or directly to the outside of the tractor center module in some less conventional paving applications. For the purposes of this description, the focus is on the manner in which bolster swing arms and the orientation of the crawlers can be changed and controlled in the more conventional paving configuration of the machine.
As is well known, tractor frames for slipform paving machines, which typically are extendable/retractable in the lateral direction to change the widths of the tractor frame and the remainder of the paving machine, have a generally rectangularly shaped center module or platform which supports, for example, the power unit including the engine for the paver, an operator platform, and the like. A side bolster is laterally movable and secured to each lateral side of the tractor frame (by means of male support tubes that telescopic in and out of the tractor center module), and bolster swing legs pivotally connect the fore and aft ends of the bolster to the respective jacking columns and crawlers of the paver. The swing legs are pivotally mounted to front and aft ends of the bolsters on vertically oriented hinge pins so that pivotal movement of the swing legs moves their end portions, which mount the jacking column and the crawlers, sideways relative to the paving direction of the paving machine and in a generally horizontal plane for increasing or decreasing the distance between the crawlers, and the distance and orientation of the crawlers relative to the tractor frame of the paving machine. Once the bolster swing legs supporting the jacking column with crawler track have the desired spacing between them and the desired orientation relative to the tractor frame, they are locked in place to prevent the crawler tracks from deviating from the desired direction/position and to absorb any existing tolerances between the bolster ends and the bolster swing legs which, if permitted to exist, allow undesired orientational deviations of the crawlers. In the past, turnbuckles and/or hydraulic cylinders were employed to prevent such tolerance-based play. To eliminate all play, two counteracting turnbuckle and/or hydraulic actuators arrangements were sometimes employed to establish a positive, immovably locked position and orientation for each crawler track.
The position fixing turnbuckles and/or hydraulic actuators were secured to mounting brackets that were bolted to a hole pattern in the front (or aft) facing surfaces of the tractor frame and the bolster swing legs and/or between the side bolster ends and the bolster swing legs. To be effective, the turnbuckles/hydraulic actuators must have a substantial angular inclination relative to the bolster swing leg. If this angular inclination becomes too small, the turnbuckles/hydraulic actuators lose effectiveness and rigidity, which, if permitted to occur, can lead to undesired deviations in the desired orientation of the crawler tracks, and if the inclination becomes too large, the distance between the point of connection of the turnbuckles/hydraulic actuators to the tractor frame and to the bolster swing leg can exceed the effective length of the turnbuckle or hydraulic actuator.
Thus, in the past, when the machine width had to be changed by a significant amount it became necessary to reposition the turnbuckle/hydraulic actuator mounting bracket along the length (in a lateral direction that is perpendicular to the travel direction) of the tractor frame to maintain the angular inclination of the turnbuckle/hydraulic actuator within an acceptable range. This was a time-consuming task that required skilled workers and, therefore, was costly. In addition, the time it takes to change the position of the mounting bracket for the turnbuckle/hydraulic actuator is a downtime for the machine during which it is out of use and cannot generate revenues.
Bolster swing legs are used so that the crawler tracks can be relatively quickly relocated in relationship to the edge of the concrete pavement that is being laid down from the normal straight-ahead position, for example to avoid obstacles in the path of the crawler tracks or to make room that may be required to allow tie bars to pass the inside of the rear crawlers and the like. One of the conventional ways of relocating the crawler track was to support the side bolster of the tractor, using the jacking column to hydraulically lift the crawler off the ground, then to use one or more turnbuckles (or one or more hydraulic actuators) to mechanically pivot the bolster swing leg with the jacking column and crawler track and, once the desired position is reached, to hold it there with a turnbuckle or steamboat ratchet (or actuator). If only one turnbuckle is used in the normal position, which is the inboard side of the bolster swing leg, the swing leg is free to move due to the inevitable manufacturing and assembly clearances and tolerances in the turnbuckle connections. These clearances are undesirable because if the swing leg is allowed to pivot or tilt under varying loads, it can adversely affect steering and elevation control. Because of this connection play, opposing turnbuckle sets were at times employed, one being located in the inboard side and one or more turnbuckles being located on the outboard side of the swing leg. In such an arrangement, after the crawler track is in the desired position, the opposing turnbuckles are tensioned (pulled) against each other to keep the swing leg from moving. This transfers all the clearance in the pin connections to one side of the hole, eliminating any possible movement in the connection. The drawback of this approach is that the outboard turnbuckles increase the overall machine profile outside the edge of concrete and therefore require more room for the machine when paving past obstacles in tight confines. If the outboard turnbuckle angle is decreased to decrease the machine profile, the effectiveness of the turnbuckles at this flat angle in holding the swing leg can decrease to almost nil. Further, every time the crawler track is relocated, all the turnbuckles must be readjusted.
Attempts have been made to eliminate the need for the outboard opposing turnbuckles by adding a hydraulic cylinder/actuator between the tractor frame and the swing leg behind the turnbuckle on the inboard of the leg. The cylinder effectively pushes the pin connection clearances to the inside of the turnbuckle connection holes and eliminates the risk of swing leg movement by keeping the hydraulic actuator pressurized.
The relocation of the bolster swing leg and crawler track in relationship to the tractor frame is further adversely affected by the need to relocate the turnbuckle connection on the tractor frame where it connects to the bolsters to which the swing leg is attached. The turnbuckle connection on the bolster swing leg side typically stays at the same connection point. In the past, the turnbuckle connection to the tractor frame posed several problems. One such problem was when the tractor frame was telescoped narrower. At wider tractor widths, the turnbuckle connects to the outboard end of the support beam of the tractor frame with a turnbuckle bracket that is bolted to the male support beam (that telescopes in and out of the tractor center module) with two or more bolts; however, if the tractor frame is telescoped narrower, the bracket will eventually interfere with the tractor center module, which prevents the further narrowing of the tractor frame. Once this point is reached, the turnbuckle mounting bracket therefore had to be unbolted from the male support beam and rebolted to the tractor center module. To maintain the optimum turnbuckle angle to the swing leg so the turnbuckle is effective in holding the leg in the desired position, the turnbuckle bracket had to be relocated along the tractor center module repeatedly, which slowed down the machine width change process during each change. The inboard turnbuckles can also interfere with other attachments required on the front and rear of the machine, such as a spreader plow that is mounted off the front of the tractor frame, which had to be disconnected and reconnected, which increases costs further. Another problem was when the swing leg complete with jacking column and crawler track is relocated to the outside of the side bolster or mounted directly to the tractor center module, in some paving applications there was no place to connect the bolster swing leg or turnbuckles (hydraulic actuators).
The relocation of the bolster swing legs and crawler track in relationship to the tractor frame is further adversely affected by the steering cylinders that typically were used on the jacking columns. The steering cylinders allow the crawler track angle to be changed in relationship to the jacking column for manual or automatic steering purposes. In the past, the steering cylinders at times protruded to the outside of the associated steering column. This is undesirable because it increases the outside width of the paving machine, which dictates and will limit how close the machine can pave next to a building or obstruction, and the stroke of the steering cylinder dictates how far the swing leg can be swung inboard or outboard. Amongst others, such a jacking column steering cylinder configuration does not allow the crawler tracks to be rotated 90° from their normal operating orientation without the time-consuming repinning or repositioning of the steering, which is a drawback.
It is however highly advantageous to rotate the crawlers to such a 90° steering position (and being able to steer the crawler track in that position) from their normal position when readjusting the machine for paving different widths, maneuvering the machine around the jobsite, or for readying the machine for transport to a different paving site. In such an event, the swing legs with jacking columns and crawlers are pivoted relative to the tractor frame until the crawlers extend in the lateral direction (which is perpendicular to the normal paving direction) of the paving machine, which minimizes the width of the paving machine so the gauge between the crawler tracks in the transport position is narrow enough to walk the machine onto a trailer and for its transportation over normal roads to a new site. This outboard 90° bolster swing leg orientation is not to be confused with rotating just the crawler tracks in the 90° position using 90° steering.
Thus, when repositioning the crawler tracks of a paving machine in accordance with conventional methods, the machine is initially appropriately supported so that a first one of the bolster swing leg-mounted crawler tracks can be lifted off the ground. The turnbuckle is then used to pivot the bolster swing leg until the jacking column and the associated crawler are at the desired (lateral) position and have the required crawler orientation. If the needed lateral movement of the crawler is too great, the turnbuckle mounting bracket must be repositioned by unbolting it from the frame and rebolting it thereto at a hole pattern located at the appropriate (lateral) point on the tractor frame or the center module. Thereafter, the turnbuckle is tightened in the new position of the crawler so that the bolster swing leg can no longer move and the orientation of the crawler is maintained. Thereafter, the crawler is lowered to the ground, it is rotated about the vertical axis of the jacking column to place it in the desired orientation, and an orientation measuring transducer is reset for the new crawler orientation to keep the crawler in the straight-ahead position. This has to be repeated for each of the typically four crawlers of the paving machine, a process that is time-consuming, costly and results in a prolonged, unproductive downtime for the machine. This cost is encountered each time the lateral position of the crawler and/or turnbuckle mounting bracket is changed and the crawlers must then be reoriented relative to the frame so that they face in the required transport direction. This procedure is also used to ready the paving machine for transportation to a new work site. In such an event, the swing legs are pivoted relative to the frame until the crawlers extend in the lateral direction (which is perpendicular to the normal paving direction) of the paving machine, which minimizes the width of the paving machine for transportation to a new site.
In an alternative approach used in the past, the crawlers and the associated jacking columns were connected to the fore and aft ends of the side bolsters and fixed mounted to the end of the parallel linkages and oriented so that the crawlers extend in the paving direction of the paving machine. The parallel linkages typically include a hydraulic actuator to assist in the crawler track relocation and to hold the crawler track in the desired position. This approach simplified the lateral adjustment of the positions/orientations of the crawlers in relationship to the tractor as compared to crawlers mounted on pivoted swing legs because no matter where the crawler track was repositioned, the crawler track always remained oriented straight ahead and the turnbuckle relocation issue went away. However, in such arrangements, the limited range of movement of the parallel linkages with hydraulic actuator limits how narrowly the machine can be collapsed for transporting it over highways (with standard highway width restrictions) to new construction sites. The ability to quickly and efficiently move the paving machine from one site to the next, which is highly desirable for the efficient use of the machine, is lost with this approach. Instead, paving machines employing such parallel linkages for the crawlers required that the tractor frame itself had to be collapsed in order to narrow the width of the machine sufficiently so that it could be transported over highways. This requires that either the paving kit itself be telescopic or that the paving kit is removed from the tractor. In either case, this could significantly increase the overall cost of the machine or the cost or time required for moving the machine and is therefore an undesirable alternative. The only way to overcome this limitation is to add a pivot hinge (with a means to lock/pin the pivot hinge in either the working or transport position) between the side bolster and the parallel linkage to allow the parallel linkage with jacking columns and crawlers to pivot outboard relative to the tractor frame until the crawlers extend in the lateral direction (which is perpendicular to the normal paving direction) of the paving machine required for loading on a trailer and transport. Of course, adding the pivot hinge with a pinning mechanism to each corner of the machine is costly, and pinning and unpinning of the hinge is time-consuming.